The present invention relates to the field of providing telephone services using asynchronous transfer mode (ATM) facilities and, in particular, to a method and apparatus for completing telephone calls between ATM subnetworks overlaid on an ATM backbone network.
Telecommunication service providers are considering using ATM as the technology of choice to consolidate their networking infrastructure under one xe2x80x9cumbrellaxe2x80x9d. An aim of this activity is to provide ATM switching systems in a networking backbone that can serve as the transport technology for traffic emanating from different sources. A second aim of this activity is to allow service providers to maximize their investment in ATM equipment. Service providers to date have primarily used ATM networks for data transport. By using ATM networks as a backbone for diverse traffic sources, service providers can expand the usage of their ATM facilities and maximize the return on capital investment made in this equipment.
In addition, the development of systems for supporting telephone services on an ATM backbone is being driven by increasing congestion arising in the PSTN/ISDN. The increasing demand for long distance services, resulting from price reductions and competition among carriers and the demand for access to Internet Service Providers (ISPs) is contributing to greater demand on available capacity in the PSTN/ISDN.
However, several challenges exist in deploying telephone service on an ATM network backbone. One of the challenges facing this network evolution involves the challenge of providing the multitude of services available in today""s PSTN/ISDN. The services provided by ATM based telephone service must remain the same as the services provided in the PSTN/ISDN. However, today""s ATM switches and networks are not enabled to support PSTN/ISDN services. ATM switches currently deployed lack both the physical infrastructure and signaling systems to support PSTN/ISDN intelligent services. Beyond simple connection control, they do not provide any of the intelligent services such as free-phone, number translation, local number portability and the myriad of supplementary services provided by a PSTN/ISDN switch. An additional consideration is the fact that regulatory requirements in some jurisdictions dictate the types of service that a service provider must offer. In addition, customers cannot be expected to accept fewer services when a service provider changes or upgrades transport facilities. A reduction in the number of services results in an immediate loss of customers, loss of revenue, and difficulties in marketing to new customers due to competition.
An ATM based system which is capable of supporting the services offered in the PSTN/ISDN is described in Applicant""s co-pending patent application entitled TRANSIT TRUNK SUBNETWORK which was filed on Sept. 23, 1998 and has been assigned U.S. patent application Ser. No. 09/158,855, the disclosure of which is incorporated herein by reference. A transit trunk subnetwork permits an ATM subnetwork to be integrated into the PSTN using interfaces referred to as xe2x80x9cMulti-Service Platformsxe2x80x9d (MSPs). The MSPs provide access to the ATM subnetwork by synchronous transfer mode (STM) switches and convert pulse code modulated (PCM) data to ATM cells and vice versa. The Transit Trunk Subnetwork also includes a call manager which communicates with STM switches through a Common channel Signaling (CCS) network, such as the Signaling System 7 (SS7) network. The call manager also communicates with the ATM subnetwork through ATM links. Consequently, the call manager is enabled to support PSTN/ISDN intelligent services, while permitting the ATM subnetwork to serve as the transport medium for bearer traffic routed between STM switches in the subnetwork.
However, in order to capitalize on the benefits offered by the Transit Trunk Subnetwork, a need exists for a method of completing calls between subnetworks without diverting the calls through the PSTN.
Accordingly, it is an object of the present invention to provide a method for completing calls between transit trunk subnetworks without diverting the calls into the PSTN.
It is a further object of the invention to provide a signaling protocol to permit call routing between transit trunk subnetworks.
It is a further object of the invention to provide a signaling protocol for completing calls between transit trunk subnetworks which uses the CCS system of the PSTN/ISDN.
It is yet a further object of the invention to provide a signaling protocol for completing calls between transit trunk subnetworks which uses backward call set up in which calls are set up by routing signaling messages from a terminating interface to an originating interface, even though CCS messages proceed in a standard forward direction.
It is another object of the invention to provide a signaling protocol for completing calls between transit trunk subnetworks in which standard Integrated Services Digital Network User Part (ISUP), SS7 signaling messages are used to complete calls so that call control signaling is effected without modifying PSTN/ISDN switches served by the subnetworks.
In accordance with the above objects, the invention provides an apparatus for transferring voice or voice grade data using ATM protocol between first and second telephone switches, respectively associated with first and second subnetworks. The first and second subnetworks are adapted to be used in the ATM backbone networks for the transfer of inter-switch bearer traffic. The first telephone switch has a first interface with the first subnetwork and the second telephone switch has a second interface with the second subnetwork. The first and second interfaces are adapted to convert PCM data to ATM cells and vice versa. The apparatus comprises a first call manager logically associated with the first subnetwork and a second call manager logically associated with the second subnetwork. The first call manager is enabled to exchange signaling messages with the second call manager containing information to effect call set up between the first and second interfaces.
In accordance with the above objects, the invention also provides a method for telephone call routing between first and second telephone switches respectively associated with first and second subnetworks using ATM protocol to transfer bearer traffic between the telephone switches. The first telephone switch has a first interface with the first subnetwork and the second telephone switch has a second interface with the second subnetwork. A first call manager is logically associated with the first subnetwork, while a second call manager is logically associated with the second subnetwork. The method comprises the steps of first routing a call request message from the first telephone switch to the first call manager. The first call manager receives the call request message and translates a dialed number extracted from the call request message to obtain routing information for the call. The first call manager also modifies the call request message to include information pertaining to the origination of the call and then forwards the modified call request message to the second call manager using the routing information. When the modified call request message is received at the second call manager, the dialed number is translated from the message to identify the second telephone switch. The second call manager uses an ATM message to advise the second interface of the modified call request message and then sends the second interface an ATM message to provide call origination and termination details. The second interface sends an ATM message to the first interface to initiate a virtual connection for transferring bearer traffic associated with the call. Thereafter, the second call manager further modifies the call request message and then forwards this further modified message to the second telephone switch to initiate seizure of a trunk to carry the call.